A basic structural unit of a silicone polymer consists of silicon-oxygen chains, through silicon atoms, side chains are connected with other various organic groups. Compared with other polymer materials, the silicone polymer has the following outstanding properties: 1. Heat-resistance: a silicone product is constituted by a main chain of silicon oxygen (Si—O) bonds, therefore, silicone products have high temperature resistance, and the molecular bond will not break or decompose at a high temperature (or irradiation). 2. Weather resistance: the main chain of a silicone product consists of —Si—O—, which has better thermostability, radiation resistance, weather resistance, and longer service life under natural environments. 3. Electrical insulation properties: a silicone product has good electrical insulation properties, its dielectric loss, withstand voltage, corona-resistance, volume resistivity and surface resistivity are all among the best in insulating materials, furthermore, its electrical performances are hardly effected by temperatures and frequencies. Thus, based on the aforementioned good properties, as a kind of silicone products, organopolysiloxane is widely used in LED package and photovoltaic industry.
CN103342816A describes a curable organopolysiloxane composition, which is used in LED lamp package and has the following advantages: excellent adhesion, high hardness, excellent thermal shock resistance, high transparency, etc.
Generally, a LED lamp package comprises a light-emitting component and a LED support, the light-emitting component is fixed on the LED support, the LED support is usually made of a metal substrate, the metal substrate is provided thereon with a silver coating, and the silver coating is used for focusing or diffusing the light of the light-emitting component. By coating the organopolysiloxane composition on the light-emitting component and the silver coating of the LED support and performing curing, the packaging of LED lamp is basically completed.
In the prior art, the LED support is usually made of copper material, a copper support has good performance in reducing resistance, increasing heat conduction and heat radiation, and extending service life, and is widely used in LED products.
As a new generation of Chip On Board (COB) substrate, a mirror finish aluminum substrate has a high reflectivity of 98% or more, with the thermoelectric separation design further reducing thermal resistance effectively, the mirror finish aluminum substrate is less susceptible to oxidation compared with a silver-plated support, and its cost is less than that of silver-plated support. COB has now been widely used in various types of lamps, and has a very good performance in both the light type and light effects.
With the development of LED industry, LED products advance toward high power, and plastic supports have been gradually unable to meet the cooling needs. A ceramic support has low expansion coefficient, high match degree with chips, high thermal conductivity, fast heat dissipation, high voltage insulation, anti-lightning shock performance, zero absorption of moisture, anti-oxidation performance, corrosion-resistance and high temperature resistance, and thus it is a high power LED support of the new generation.
However, when the organopolysiloxane composition in the prior art is applied to high power supports, such as a mirror finish aluminum support, a ceramic support, a copper COB support or an integrated support, there exists a problem of heat resistance of silicon, which is mainly manifested as cracking of silicon caused by heat produced by an LED lamp during a process of long-term and high-power use, and affects the life span of an LED lamp.